When Nova Delphini 2013 emerged last August, I pondered the curious illusion of its stellar appearance. What we see as a “new star” actually is an enormous shell of hydrogen gas exploding off the surface of a white dwarf star in a close binary system. The nova’s shell appears stellar because it lies at a great distance — in this case some 11,400 to 17,900 light-years from Earth. Sometimes, when a nova cools and fades, major observatories are able to image its structure — rings and shells that look much like those displayed by planetary nebulae.

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